doc/uImage.FIT/x86-fit-boot.txt

9 Generally Linux x86 uses its own very complex booting method. There is a setup
10 binary which contains all sorts of parameters and a compressed self-extracting
11 binary for the kernel itself, often with a small built-in serial driver to
15 understanding is that an x86 CPU (even a really new one) starts up in a 16-bit
22 mode was something of a challenge, so putting this logic in the kernel seemed
35 - Locating and tacking on a device tree and ramdisk
38 doesn't make a huge amount of sense. Any boot loader worth its salts already
40 the layout of memory, has a serial driver, can decompress things, includes an
42 all these features in a Linux wrapper caters for the lowest common
43 denominator: a boot loader which consists of a BIOS call to load something off
44 disk, followed by a jmp instruction.
48 or in the boot loader rather than adding a self-relocator to put it in the
51 As a result, the x86 kernel boot process is needlessly complex. The file
52 format is also complex, and obfuscates the contents to a degree that it is
53 quite a challenge to extract anything from it. This bzImage format has become
66 Note: these instructions assume a 32-bit kernel. U-Boot also supports directly
67 booting a 64-bit kernel by jumping into 64-bit mode first (see below).
69 You can build the kernel as normal with 'make'. This will create a file called
70 'vmlinux'. This is a standard ELF file and you can look at it if you like:
138  30 .debug_abbrev 0022a83b  00000000  00000000  04ade647  2**0
155 helps by providing a head start.
161 use of a relocatable kernel.
166 Create a FIT
169 To create a FIT you will need a source file describing what should go in the
171 the 'arch' value for booting 64-bit kernels if desired. Put this into a file
174 Note that setup is loaded to the special address of 0x90000 (a special address
176 saw above). This means that you will need to load your FIT to a different
180 In that example the kernel is compressed with lzo. Also we need to provide a
183    # Create a flat binary
189    # Build a FIT image
195 You can take a look at the resulting fit file if you like:
229 To make it boot you need to load it and then use 'bootm' to boot it. A
230 suitable script to do this from a network server is:
239 If you want a ramdisk you can add it as normal with FIT. If you want a device
254 6. It makes x86 more like other architectures in the way it boots a kernel.